This invention relates generally to a system to automatically refill a liquid from a bulk container to a smaller receiving container without contamination. More specifically, it relates to a modular system providing fresh liquid chemicals through an automatic refill to a plurality of bubbler ampules in their corresponding liquid source temperature controllers that supply a vapor to a corresponding number of diffusion furnaces.
Source liquid chemical temperature controllers have been utilized in the semiconductor and fiber optics industries to supply chemicals directly or in carrier gases that are saturated with the particular chemical as a function of the ampule's or liquid chemical receiving container's, temperature. Various ultra high purity liquid chemicals, including those commonly called dopants, are required for these industries.
The ampules in liquid temperature controllers, commonly called bubblers, must be periodically replaced based on the usage of the ultra high purity source chemical. The amount of chemical used is a function of the degree of saturation of the carrier gas carrying the chemical to the diffusion furnace and the quantity of carrier gas used. This, in turn, is a direct function of the bubbler ampule temperature. Typical inert carrier gases are nitrogen, argon, or helium. Some typical chemicals utilized in bubblers are licate 1,1-trichloroethane (TCA), tetraethylorthosilicate (TEOS), phosphorous oxychloride (POCl.sub.3), and the dopant chemicals trimethylborate and trimethylphosphite.
In the past, when the chemical in the bubbler ampule was depleted, typically the ampule had to be removed from the temperature controller and refilled at a remote site. An attempt to create a commercial system to refill the ampules within the temperature controller was developed by the J. C. Schumacher Company and called the CRS chemical refill system. This system refills empty quartz bubbler ampules batchwise in the temperature controllers.
In the typical semicondutor prior art process, a replacement bubbler ampule, with fresh chemical, is inserted into the liquid temperature controller. This replacement of the chemical, however, requires physical removal of the depleted ampule from the liquid temperature controller and suffers from the inability to operate both the diffusion furnace and the liquid temperature controller for a period of time. The temperature of the replacement liquid chemical is lower than that required for operation by this prior art replacement procedure. Normally the furnace tube temperature is then lowered during these periods of non-operation. Prior to recommencing use of the replenished chemicals, both the bubbler ampule and the diffusion furnace have to be reheated to their operating temperatures. Further, test samples are routinely run through the process to ensure that the replenished chemical is not contaminated prior to resuming the production operation. The total liquid chemical replacement process can take from two to eight hours, depending upon the chemical involved and the end use.
In the prior art Schumacher chemical refill system, the same problem was present with the low temperature of the replacement chemical and resultant inability to operate the diffusion furnace until the chemical was reheated. This system had the additional disadvantage of being oversized for use in clean rooms.
Automatic liquid replacement or refill systems for liquids have been utilized in other industries, but where the purity requirements of the liquid are far less stringent. Generally, however, these replacement systems have been based upon measuring the weight of the liquid in the receiving container at comparative points in time or by using a time filling sequence to ensure the proper volumetric quantity is delivered. None of the systems were designed to work with the stringent requirements needed for ultra high purity chemicals in the semiconductor industry.
Additionally, automatic chemical refill systems servicing a multiple number of temperature controllers and their bubbler ampules from one central refill control system have suffered from the problem that when one temperature controller has experienced problems or malfunctioned in the system, all of the refill lines have had to be shutdown until the problem is corrected. Most chemical vapor deposition systems are capable of operating up to four temperature controllers concurrently to supply vapors to a corresponding number of diffusion furnaces. Thus, a repair required of just one temperature controller in the refill system can cause all of the temperature controllers in the system to be shutdown.
These problems are solved in the design of the present refill system by providing a Modular automatic refill system where the temperature controllers operate completely independently from each other to automatically refill the bubbler ampule in a liquid temperature controller without removing the ampule from the controller.